Single precision big endian float values to JavaScript floats

Question

I'm receiving float values from an Arduino in this format:

'0000803E' = 0.25
'00002041' = 10
'68414843' = 200.2555

In Java (Processing) I can do this:

float decodeFloat(String inString) {
  byte [] inData = new byte[4];

  if(inString.length() == 8) {
    inData[0] = (byte) unhex(inString.substring(0, 2));
    inData[1] = (byte) unhex(inString.substring(2, 4));
    inData[2] = (byte) unhex(inString.substring(4, 6));
    inData[3] = (byte) unhex(inString.substring(6, 8));
  }

  int intbits = (inData[3] << 24) | ((inData[2] & 0xff) << 16) | ((inData[1] & 0xff) << 8) | (inData[0] & 0xff);
  return Float.intBitsToFloat(intbits);
}

Is there a utility NPM package/function/library which can do the transformation or how can I do this in JS?

Nope, this is strictly JS related. It doesn't matter whether the data comes from Arduino/a floppy disk or a cereal box. — Hedge
– Hedge, Commented Dec 20, 2015 at 20:19

Hedge · Accepted Answer · 2015-12-21 10:15:43Z

0

I was able to do the conversion partly myself and with the aid of the jspack package.

const jspack = require('jspack').jspack;

function decodeFloat(inString){
        let inData = [];

        inData[0] = parseInt(inString.substring(0, 2), 16);
        inData[1] = parseInt(inString.substring(2, 4), 16);
        inData[2] = parseInt(inString.substring(4, 6), 16);
        inData[3] = parseInt(inString.substring(6, 8), 16);

        return jspack.Unpack('<f', inData)[0];

}

let hexFloats = ['0000803E','00002041','68414843'];

console.log(hexFloats.map(decodeFloat)); // [ 0.25, 10, 200.2554931640625 ]

edited Dec 21, 2015 at 10:15

answered Dec 21, 2015 at 10:05

Hedge

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